System and method for evaluating and determining color in gemstones

ABSTRACT

A system for the automatic grading of a cut/polished gemstone (SUT) includes an enclosure with a stage for mounting the cut/polished SUT. The enclosure further includes one or more sources of broadband visible (BBV) light, the sources of BBV light being controllable by a programmable controller; an image sensor for capturing a plurality of images of a mounted SUT, and one or more sources of UV light mounted within the enclosure. The controller captures images of the mounted SUT from one or more selected angles relative to the sensor elevation axis and relative to the position of the SUT on the stage rotation axis; an image capturing module is configured for processing the one or more images; and, a light grade calculation module is configured for grading the cut/polished SUT using light indicative parameters from at least a part of the one or more images captured.

BACKGROUND OF THE PRESENT INVENTION

The color of a gemstone, and especially a diamond, is one of its majorattributes which affects its value. The less color a diamond has, thehigher its value. A perfect crystalline diamond with no structural orchemical impurities is basically colorless.

Gemologists judge a diamond's color through visual perception bycomparing a diamond of interest in a “color bath” with a set of masterstones which define the standard colors on a scale of D to Z, runningfrom colorless to yellow, respectively. For example, a trainedgemologist (under ideal standardized lighting conditions) during suchcomparison will grade a stone color as E if he/she sees the stone in a“color bath” as more yellow than the D master stone but less yellow thanthe F master stone.

There were many attempts to develop a color grading machine to automatethe color grading process. Two known strategies to measure color are:colorimetry and spectrophotometry. Shipley offered a colorimetric systemhaving a light source with interchangeable blue and yellow opticalfilters and a light detector. The optical transmission of filtered lightthrough a target stone could then be measured and compared with a lookuptable to grade the stone color along the D to Z scale. One of the maindeficiencies of this system was that the light source which did notprovide the type of daylight conditions which have been the standard forvisual color analysis. Improvements on the Shipley system offered bysuch entities as Eickhorst, Okuda, Austron and Gran, and although theyused more modern light sources and photo detectors, they were designedto direct light into the table and crown.

Spectrophotometers for measuring a diamond color have been offered byOkazaki, Zeiss-Gubelin and later by Rennilson-Hale, Lamdaspec, Gran,Adamas and others. These systems detect and analyze the full spectrum oflight. However. They have failed to replace human visual diamondanalysis.

GIA U.S. Pat. No. 6,473,164 discloses a technology for color measurementof diamonds based on daylight approximating lighting impinged on thepavilion side of the diamond and then by measuring light coming out ofthe pavilion at a specific angle. Measurements are compared tohistorical precedents or converted into CIE color space. According tothe '164 patent, a diamond's visual appearance to the human eye underdaylight approximating light is a primary indicator of the quality ofthe diamond.

GIA U.S. Pat. No. 9,678,018 discloses hyperspectral imaging toapproximate the visual perception of the human eye by filtering outwavelength ranges which are less perceivable by a human eye.

GIA US publication No. 20160290925 discloses an automated instrument forgrading a gemstone's fluorescence color using a UV lighting system tocapture fluorescent images of an illuminated gemstone.

De Beers WO2016203210 discloses calculating color vectors from anexpression of the chrominance values of a gemstone pixel in chrominancespace. The color vector extending in chrominance space from stone pixelshaving a relatively high luminance value to stone pixels havingrelatively low luminance values. A direction of the color vectorprovides a pointer towards the pixels representing light which hastravelled along long light paths through the stone and therefore haverelatively low luminance.

Sarine 9,519,961—Sarine Loupe—discloses a volumetric 3D model. Thisdisclosure is herein incorporated by reference into this application inits entirety.

U.S. Pat. No. 6,239,867 discloses an apparatus and method for grading,testing and identifying gemstones that includes a number of lightsources, including UV light for fluorescence analysis as well as ringlights) mounted within an enclosure to illuminate a mounted gemstonefrom below and from above. A CCD camera is mounted on a linearpositioner to travel from first to second positions to focus the CCDcamera the gemstone image.

U.S. 2012/0007971 discloses methods and systems for imaging cutgemstones that includes a number of compact florescent light bulbs orLEDs mounted within a cabinet to provide neutral and homogeneouslighting. There is no mention of providing UV lighting to illuminate amounted gemstone. An image sensor is mounted on a movable arm thatcaptures images of a mounted gemstone based on illumination from thelight bulbs or LEDs.

U.S. 2016/0290925 discloses an apparatus and method for fluorescencegrading of gemstones that includes one or more UV light sources and athermal sensor for adjusting the intensity of the UV light sources.

SUMMARY OF THE PRESENT INVENTION

In an aspect, a system for the automatic grading of a cut/polisheddiamond or other stone (hereinafter sometimes referred to as a “stoneunder test” or SUT) includes an enclosure, the enclosure including aholder for supporting the cut/polished stone, the holder comprising acentral axis, the holder being rotatable about its central axis by arotation device; the enclosure further includes one or more sources ofbroadband visible light (BBV), the sources of BBV light beingcontrollable by a programmable controller, as well as an image sensorfor capturing a plurality of color-measurement images of the mountedgemstone; the image sensor is mounted on an actuator for rotation on aplane about the central axis; one or more sources of UV light aremounted on the actuator in the vicinity of the image sensor (orelsewhere), whereby the sensor is programmed by the controller tocapture images of the mounted stone from one or more selected anglesrelative to the sensor axis and relative to the central axis. Thecontroller may be configured to activate the one or more sources of UVlight, the one or more sources of BBV light, the rotation device, theactuator and the image sensor to capture one or more color images of thecut/polished stone. The system also may include an image capturingmodule configured for processing the one or more color images; and, acolor grade calculation module configured for color grading thecut/polished stone using color indicative parameters from at least apart of the one or more color images captured.

In another aspect, a method for the automatic grading of a cut/polishedgemstone (SUT) includes: providing an enclosure, the enclosure includinga stage for mounting the cut/polished SUT, the holder comprising acentral axis, the stage being rotatable about a stage rotation axis by arotation device; the enclosure further comprising one or more sources ofbroadband visible light (BBV), the sources of BBV light beingcontrollable by a programmable controller; providing an image sensor forcapturing a plurality of color-measurement images of a SUT mounted onthe stage; the image sensor being mounted on an arm, the arm beingrotatable around a sensor elevation axis, the sensor elevation axisbeing normal to the stage rotation axis; providing one or more sourcesof UV light within the enclosure; providing an image capturing moduleconfigured for processing the one or more images; and, providing a lightgrade calculation module configured for grading the cut/polished SUTusing light indicative parameters from at least a part of the one ormore images captured; wherein the method comprises: the controllerprogramming the sensor to capture images of the mounted SUT from one ormore selected angles relative to the sensor elevation axis and relativeto the position of the SUT on the stage rotation axis; the controller:activating the one or more sources of BBV light, activating the one ormore sources of UV light, rotating the SUT around the stage rotationaxis, and causing the image sensor to capture one or more images of thecut/polished SUT; the image capturing module processing the one or moreimages; and, the grade calculation module grading the cut/polished SUTusing light indicative parameters from at least a part of the one ormore images captured.

In an aspect, the programmable controller is configured to cause theimage sensor to capture light in the form of images around the sensorelevation axis from impingement of one or both of the BBV and the UVlight sources at a plurality of different angular positions with respectto 0 degrees, wherein 0 degrees is normal to the stage rotation axis ofthe stage. Further, the controller is configured to cause the imagesensor to capture at 0 degrees, at X degrees, and at Y degrees, whereinY≠X≠0 degrees. Yet further, the controller is further configured tocontrol the power level of the one or more BBV sources, the controllerbeing further configured to cause the image sensor to capture images atmore than one power levels of the BBV sources.

In a further aspect, the system further comprises a memory system, andwherein the programmable controller is configured to store the capturedimages in the memory system for processing. The images captured arestored in the memory system in a RAW format or a non-RAW format.

In yet another aspect, the programmable controller is configured to scanthe SUT prior to the controller being configured to capture images forgrading, the scan of the SUT causing the controller to create a 3Dvolumetric model of the SUT. Further, the programmed controller isconfigured to: (a) for captured image frames, average the color-spacevalues of one or more captured frames to calculate reference values ofwhite balance of the one or more captured frames; and, (b) if a 3Dvolumetric model of the SUT has been created, select pixels. Also, thecontroller may be configured to differentiate the selected pixels eitherby: (a) creating histograms for the selected pixels captured at thedifferent angular positions and by the controller being configured todivide the selected pixels by their levels of intensity, whereby theaverage color is calculated. (b) segmenting an SUT into distinctregions, and using selected pixels captured within said regions, at thedifferent angular positions, whereby the average color is calculated.

In a further aspect, the controller may be configured to calculatecolorspace values of one or more frames of the SUT under the one or moreUV light sources, the controller further being configured to add thecalculations to the average color calculations from the BBV sources andwherein color grading is corrected based upon measurement under UVillumination. Further, the controller may be configured to compare theaverage color calculations of a SUT to a calibrated lookup tablecontaining data on calibrated SUTs with known SUT whiteness and to matchthe SUT calculations to those of the calibrated SUTs to determine agrade level of the SUT.

In an aspect of the method, the programmable controller causes the imagesensor to capture light in the form of images from impingement of one orboth of the BBV and the UV light sources at a plurality of differentangular positions with respect to 0 degrees, wherein 0 degrees is normalto the stage rotation axis of the stage. The controller may cause theimage sensor to capture at 0 degrees, at X degrees, and at Y degrees,wherein Y≠X≠0 degrees.

In a further aspect, the programmable controller is configured tofurther scan the SUT at a central area of the SUT and at least one otherarea of the SUT. The system of claim 25, wherein the programmablecontroller is configured to further scan one or more of: (a) at leastone peripheral area between the central area and one of the boundariesof the SUT and (b) at least one area above or below the central area.

In yet another aspect, the image sensor may be a color image sensor. TheBBV light comprises white light. The system of claim 1, wherein the BBVlight comprises a plurality of similar wavelength LEDs producing lightin the broadband range. The BBV light comprises a plurality of similarwavelength LEDs producing light in the broadband range. Further, the BBVlight may comprise a plurality of dissimilar wavelength LEDs that, whencombined, produce light in the broadband range.

In a further aspect, the colorspace values may be RGB values. Inaddition, the one or more sources of UV may be mounted on the arm in thevicinity of the image sensor. The one or more sources of UV are mountedon the arm in the vicinity of the image sensor. The step wherein thegrade calculation module grading the cut/polished SUT further adjuststhe grade calculation based on taking into account the simultaneouscontrast effect. Further, the controller is further configured to adjustthe operation of the grade calculation module to grade the cut/polishedSUT to take into account the simultaneous contrast effect.

In yet another aspect, the one or more sources of UV light are mountedon the stage for mounting the SUT. Also, if a 3D volumetric model hasbeen created, the programmed controller is configured to use the 3Dvolumetric model to one or more of: (a) adjust one or more of multipleangles set for image capture, (b) determine which of a plurality ofsources of UV light to activate, (c) determine which of a plurality ofsources of BBV light to activate, and (d) determine the intensity atwhich to activate each of the selected BB V/UV sources.

In an aspect, the steps of the programmed controller using the 3Dvolumetric model one or more of: (a) adjust one or more of multipleangles set for image capture, (b) determine which of a plurality ofsources of UV light to activate, (c) determine which of a plurality ofsources of BBV light to activate, and (d) determine the intensity atwhich to activate each of the selected BBV/UV sources. The cut/polishedSUT may be a diamond.

In another aspect, a method for the automatic grading of a cut/polishedstone (SUT) includes: providing an enclosure, the enclosure including astage for mounting the cut/polished SUT, the holder comprising a centralaxis, the stage being rotatable about a stage rotation axis by arotation device; the enclosure further comprising one or more sources ofbroadband visible light (BBV), the sources of BBV light beingcontrollable by a programmable controller; providing an image sensor forcapturing a plurality of color-measurement images of a SUT mounted onthe stage; the image sensor being mounted on an arm, the arm beingrotatable around a sensor elevation axis, the sensor elevation axisbeing normal to the stone stage rotation axis; providing one or moresources of UV light within the enclosure; providing an image capturingmodule configured for processing the one or more images; and, providinga light grade calculation module configured for grading the cut/polishedSUT using light indicative parameters from at least a part of the one ormore images captured; wherein the method comprises: the controllerprogramming the sensor to capture images of the mounted SUT from one ormore selected angles relative to the sensor elevation axis and relativeto the position of the SUT on the stage rotation axis; the controller:activating the one or more sources of BBV light, optionally activatingthe one or more sources of UV light, rotating the SUT around the stagerotation axis, and causing the image sensor to capture one or moreimages of the cut/polished SUT; the image capturing module processingthe one or more images; and, the grade calculation module grading thecut/polished SUT using light indicative parameters from at least a partof the one or more images captured.

In a further aspect, a method for the automatic grading of acut/polished gemstone (SUT) includes: providing an enclosure, theenclosure including a stage for mounting the cut/polished SUT, theholder comprising a central axis, the stage being rotatable about astage rotation axis by a rotation device; providing an image sensor forcapturing a plurality of color-measurement images of a SUT mounted onthe stage; the image sensor being mounted on an arm, the arm beingrotatable around a sensor elevation axis, the sensor elevation axisbeing normal to the SUT stage rotation axis; providing one or moresources of broadband visible (BBV) light within the enclosure, the oneor more sources of BBV light being controllable by a programmablecontroller; providing an image capturing module configured forprocessing the one or more images; and, providing a light gradecalculation module configured for grading the cut/polished SUT usinglight indicative parameters from at least a part of the one or moreimages captured; wherein the method comprises: the controllerprogramming the sensor to capture images of the mounted SUT from one ormore selected angles relative to the sensor elevation axis and relativeto the position of the SUT on the stage rotation axis; the controller:activating the one or more sources of BBV light, rotating the SUT aroundthe stage rotation axis, and causing the image sensor to capture one ormore images of the cut/polished SUT; the image capturing moduleprocessing the one or more images; and, the grade calculation modulegrading the cut/polished SUT using light indicative parameters from atleast a part of the one or more images captured.

In another aspect, the BBV light source is controlled with the help of atemperature measuring sensor or sensors. The temperature of the lightsources is actively controlled by conventional devices not shown. Thetemperature of the light sources may be actively controlled to within1-3° C. or to within 0.1-1° C. The temperature of the BBV light sourcesis actively controlled to within 0.1-1° C.

In another aspect, the temperature of the UV light sources is activelycontrolled to within 1-3° C. or to within 0.1-1° C. Also, thetemperature of the UV light sources is actively controlled. In addition,the BBV light source is controlled with the help of a light intensitymeasuring sensor or sensors (not shown). The UV light source iscontrolled by a temperature measuring sensor or sensors (not shown).

In an aspect, a correction may be applied to the image capturingprocess, based on a reading from one or more light intensity measuringsensors (conventional and not shown) and a correction is applied is tothe image sensor gain, based on a reading from one or more lightintensity measuring sensors.

In yet another aspect, the correction may be applied to the image sensorgain, in a known manner, based on a reading from one or more lightintensity measuring sensors. A correction applied may be to the imagesensor exposure time, based on a reading from one or more lightintensity measuring sensors. A correction may be applied to the capturedimage, based on the reading from one or more light intensity measuringsensors. A correction may be applied to the image capturing process,based on a reading from one or more temperature measuring sensors(conventional but not shown) mounted in or in the vicinity of theenclosure. A correction may be applied to the image sensor gain, basedon a reading from one or more temperature measuring sensors. Acorrection may be applied to the image sensor exposure time, based on areading from one or more temperature measuring sensors or based on areading from one or more temperature measuring sensors.

Also, in an aspect, a correction is applied is to the image sensor gain,based on a reading from one or more temperature measuring sensors or tothe image sensor exposure time, based on a reading from one or moretemperature measuring sensors. A correction may be applied to thecaptured image, based on a reading from one or more temperaturemeasuring sensors.

In an aspect, any data collected during the measurement under UVillumination may also be used by processing by the controller forgrading the fluorescence of the SUT.

In another aspect, a system for the automatic grading of a cut/polishedgemstone (SUT) includes an enclosure, the enclosure including a stagefor mounting the cut/polished SUT, the stage comprising a stage rotationaxis, the stage being configured to be rotatable about the stagerotation axis by a rotation device; the enclosure further comprising oneor more sources of broadband visible (BBV) light, the sources of BBVlight being controllable by a programmable controller; an image sensorfor capturing a plurality of images of a mounted SUT; the image sensoris mounted on an arm, the arm being rotatable around a sensor elevationaxis, the sensor elevation axis being normal to the stage rotation axis;one or more sources of UV light mounted on the arm in the vicinity ofthe image sensor; the sensor is programmed by the controller to captureimages of the mounted SUT from one or more selected angles relative tothe sensor elevation axis and relative to the position of the SUT on thestage rotation axis; Further, the controller is configured: to activateand control the power level of one or more of the one or more sources ofBBV light, to activate and control the power level of one or more of theone or more sources of UV light, to rotate the SUT around the stagerotation axis, to rotate the arm around the sensor elevation axis and tocause the image sensor to capture one or more images of the cut/polishedSUT; an image capturing module configured for processing the one or moreimages; and, a light grade calculation module configured for grading thecut/polished SUT using light indicative parameters from at least a partof the one or more images captured.

In yet another aspect, a method for the automatic grading of acut/polished gemstone (SUT) includes: providing an enclosure, theenclosure including a stage for mounting the cut/polished SUT, theholder comprising a central axis, the stage being rotatable about astage rotation axis by a rotation device; the enclosure further includesone or more sources of broadband visible light (BBV), the sources of BBVlight being controllable by a programmable controller; providing animage sensor for capturing a plurality of color-measurement images of aSUT mounted on the stage; the image sensor being mounted on an arm, thearm being rotatable around a sensor elevation axis, the sensor elevationaxis being normal to the stage rotation axis; providing one or moresources of UV light mounted on the arm in the vicinity of the imagesensor; providing an image capturing module configured for processingthe one or more images; and, providing a light grade calculation moduleconfigured for grading the cut/polished SUT using light indicativeparameters from at least a part of the one or more images captured. Themethod comprises: the controller programming the sensor to captureimages of the mounted SUT from one or more selected angles relative tothe sensor elevation axis and relative to the position of the SUT on thestage rotation axis; the controller: activating and controlling thepower level of one or more of the one or more sources of BBV light,activating and controlling the power level of one or more of the one ormore sources of UV light, rotating the SUT around the stage rotationaxis, and causing the image sensor to capture one or more images of thecut/polished SUT; the image capturing module processing the one or moreimages; and, the grade calculation module grading the cut/polished SUTusing light indicative parameters from at least a part of the one ormore images captured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an embodiment of the hardware portion of the presentinvention.

FIGS. 1B, 1C and 1D graphically illustrate typical power distributionsof phosphor-based white LEDs.

FIGS. 2A through 2C illustrate one embodiment of a technique for imaginga stone to determine volumetric characteristics.

FIG. 3 is a flow chart of a series of operations on a SUT to determineits color characteristics.

FIG. 4 is a graphical illustration of a phenomena known as the“simultaneous contrast effect”.

FIGS. 5A-5C illustrate another embodiment of another technique forimaging a stone for acquisition of color images taken at 0 degrees, 30degrees and 45 degrees in the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

As may be appreciated from the prior art, a gemstone's (and particularlya diamond's) visual appearance to the human eye under natural ordaylight-approximating light is the gold standard of the industry whenit comes to color grading. As such, existing color measuring devices arebased on their ability to approximate daylight lighting and be as closeas possible to CIE Standard Illuminant for Colorimetry D65.

These prior art systems generally use incandescent light bulbs such asTungsten lamps, metal halide lamps, white LED lights, laser inducedwhite light, Xenon flash lamps or fluorescent Halogen lamps having highcolor temperature (approximately 6500K) and high rendering index (CRI),preferably at least 95. However, no commercially available lamp, as oftoday, can generate light identical to standardized daylight. Typical“White” LEDs have about 80 CRI and are therefore inadequate to beemployed as a source for daylight approximation. Moreover, typical LEDsare characterized by a discrete spectrum with two band spectrumemissions. A first band may occur at about 450 nm and a second band atabout 600 nm.

It is to be understood that instead of using a plurality of LEDs withspecific light bands in the ranges discussed, a plurality of narrowwavelength LEDs of somewhat differing wavelength ranges may be used, solong as the overall light effect is, when mixed, in the desiredbroadband.

A typical spectral power distribution of phosphor-based white LEDs isshown in FIGS. 1B, 1C and 1D. An automated color grading system whichuses such LEDs, however, may underestimate the yellowish color of adiamond and overestimate its grade and value. Therefore, preferably,light from the entire visible spectrum should be used to more accuratelygrade the color of a diamond, and such light can be obtained byutilizing new LED technology developed for accurate color rendering.

According to this aspect of the invention, and as shown in FIG. 1, thereis provided a closed chamber 10 which is configured to hold a gemstoneand rotate it on rotatable stage 12. Embedded in the walls of thechamber are arrays of BBV LEDs (not shown) covered by light diffusers14. Each array of LEDs is controlled by a programmable controller andcan be turned on and off separately and is configured to apply dynamicillumination of BBV light with high intensities and homogenously aroundthe centered stone stage. The light generated by the BBV LEDs is used asa base line for color grading process as will be described below.

Furthermore, since in many situations, the illumination surrounding agemstone may also include non-visible (e.g. UV) wavelengths, which mayinfluence the observer's perception of a stone's color, a colormeasurement system or method may benefit from incorporating suchillumination to account for these otherwise unmeasurable effects. Inaddition, the closed chamber may include one or more UV LEDs 16A and 16Bas seen in FIG. 1A. The UV LEDs 16A and 16B are mounted on a rotatablearm 18 that may rotate on a stone stage rotation axis in directions 15about a center 20 and a sensor elevation axis and move in directions 19.The UV LEDS are mounted in the vicinity of the sensor 22 and are shownin FIG. 1A as being mounted on either side of the sensor. However, theLEDs may be mounted anywhere else within the enclosure suitable so thatthe stone is adequately illuminated by the LEDs, including mounting theLEDs or some of the LEDs on the stage itself.

A camera or other type sensor 22 may be mounted near to the LEDs 16, maymove on a sensor focusing axis in directions 23 to capture images from adiamond or other gemstone (not shown) mounted on the top portion 17 ofrotating stage 12. In this manner, the LEDs 16A and 16B with camera orsensor 22 may rotate around center 20 in directions 19 on the sensorelevation axis and capture images from a mounted gemstone at a varietyof angles, to be discussed below. A benefit of this arrangement is thatthe light emitting from the UV LEDs is better directed to reflect UVlight back from the SUT at all the positions the sensor 22 is movableabout the SUT than if the UV LEDs were mounted elsewhere within thechamber, such as along the inner walls of the chamber.

A diamond's color differences along the D to Z scale are very small andare usually seen by a professional, trained and experienced expert. Inparticular, color differences between D to F grades are very close.However, differences in grades D to F possess very dramatic effects on astone's price. Color differences are calculated in color space as ΔE. ΔEis appreciated as reflecting a just noticeable difference (JND) andunempirically valued by CIELAB as 1. However, the difference betweendiamond color grade D and E is about 0.6 ΔE which is less than the JNDfor average persons.

In other words, the average person will see and perceive diamonds gradedas D and those graded as E in much the same way, although their pricesare very different. A conventional color image sensor is no better thana human eye in discerning color differences.

It is therefore another aspect of the present invention to use an imagesensor with improved radiometric resolution. Moreover, using a regularviewing screen there is no way to present the measured data and it isanother aspect of the invention (to be described below) as to the waysthat the raw data is processed, analyzed and eventually provides anaccurate color grading for a gemstone.

Another aspect of the present invention is 3D volumetric modeling of thediamond. This modelling, which may or may not be used in connection withthe invention of the present invention, is described in theaforementioned U.S. Pat. No. 9,519,961, which is incorporated byreference herein in its entirety. Obtaining a volumetric model of theSUT may be beneficial in evaluating the color of that same stone whenspecific areas of the stone are used for such color evaluation as willbe described below.

Gemologists grade a diamond color based on the light emitting from thepavilion after a single reflection—so-called “clean” light. Multipleinternal reflected light beams may have different color tones andtherefore less accurately represent the real color of the diamond.Therefore, according to this aspect of the invention the color gradingsystem may measure single reflected light for the color evaluation.Based on the 3D model as mentioned above, or other image processingmodelling, stone masks are calculated from which color evaluation may bedone.

As the color of a diamond is a deciding factor in its value, there isconsiderable financial motivation to circumvent any automated colorevaluating system in order to apply a higher grade. One easilyimplementable, and therefore potentially common approach for this typeof fraud would be to measure the color of a higher grade stone andattribute it to another, or many other lower grade diamonds. Therefore,in another aspect of this invention, the system would possess means bywhich to verify the identity of the SUT. This could be accomplished, forexample, by utilizing the 3D volumetric model of the SUT and comparingit to a known reference for the same stone. Another possible method bywhich to verify the identity of the SUT would be to read an inscribedcode on the girdle of the diamond. Yet another method could be tocompare surface features of the SUT to a known reference. Any, or anycombination of these approaches for stone traceability could be used toa) identify the diamond before and during scanning, b) record theuniquely identifiable information of the diamond, and c) verify itsidentity at a future point in time, thus greatly reducing theopportunity for grading fraud. One system and method of uniquelyidentifying a gemstone is U.S. application Ser. No. 15/564,565, filedOct. 5, 2017, assigned to the assignee of the present invention, theentire contents of which is herein incorporated by reference.

A First Embodiment to Determine Color

In a first embodiment, one specific methodology to determine colorincludes the following general steps:

(1) first scanning a cut/polished diamond or other stone to capture afirst plurality of images at different positions of the cut stone aboutits stage's rotational axis, and using these images to calculate avolumetric 3D model of the stone, for example, using the techniquesdisclosed in the aforesaid U.S. Pat. No. 9,519,961, and

(2) next, performing a second scanning of the cut diamond at an angularposition of the image sensor which may be different from that in

the first scanning, to capture a second plurality of images at differentpositions of the cut stone about its stage's rotational axis, thenprocessing these images by an image capturing module within the system,using at least a part of volumetric data derived from the imagesobtained in the first scanning.

As used herein, the first scanning will be referred to as ‘modelingscanning’. The first images used to calculate a volumetric/3D model ofthe diamond will be referred to as ‘modeling images’. The secondscanning will be referred to as ‘color-measurement scanning’ and thesecond images used for color determination

It will now be described how areas are selected in the image of thecut/polished diamond in each color-measurement image, by the imagecapturing module, when it processes the color-measurement images, forthe use of color indicative parameters of these areas in the measurementof the cut/polished diamond's color.

First, each selected area has a closed circumference separating it fromthe remainder of the image of the cut stone and, optionally, from thebackground image or holder image, in case a portion of the abovecircumference coincides with a corresponding portion of the respectiveboundary of the image of the cut/polished stone in the color-measurementimage. Each of the selected areas can be analyzed individually or inconjunction with another area.

Second, the areas which may be selected may, for example, include acentral area, and at least one additional area, the additional areabeing optionally constituting either at least one peripheral areadisposed between the central area and one of the above boundaries, or anarea disposed above or below the central area. It is to be noted herethat what is considered to be a “central area”, a “peripheral area” anda “boundary” may be affected by the physical structure of the stoneitself as well as perhaps by the 3D model of the stone itself.

The use of the combined selection of the central area with at least oneadditional area for color grading of a cut diamond, according to thepresently disclosed subject matter, is connected to the surprisingeffect that such selection achieves a more accurate result than thatobtained based solely on selection of a central area, i.e. a result thatis closer that obtained by a human eye during color grading. Onepossible explanation to this surprising effect is presented below.

It is known that determining a color of a diamond is normally performedby examining a central area of its part remote from its table facet,such as a central area of a pavilion in a round cut diamond. Thiscentral area is considered to reflect the true color of the diamond,since it has the least internal reflections when looking through itsside and thus has the brightest color and which best represents the truestructure of the diamond.

However, the human eye can be expected to be affected during theexamination of the central area by the color of the areas adjacent thecentral area, due to a phenomena known as the ‘simultaneous contrast’effect, which is the enhancement or diminishment, relative to normal, ofperception, cognition or related performance as a result of simultaneousexposure to a stimulus of lesser or greater value in the same dimension(here, normal perception, cognition or performance is that which wouldbe obtained in the absence of the comparison stimulus—i.e., one based onall previous experience).

FIG. 4 exemplifies this “simultaneous contrast” phenomena byillustrating two identical grey rectangles, an upper rectangle 900 a anda lower rectangle 900 b. Each of these rectangles is surrounded by abackground, a dark and a light background respectively. To the humaneye, the upper rectangle 900 a appears to be a lighter grey than thelower one due to the different backgrounds.

When selecting the central and additional areas, the uppermost surfaceof the stage, which is in contact with the surface of the gemstone, canbe used as a reference plane, and the 3D model of the gemstone in thestage can be used to determine in the color-measurement images the realposition of this plane. In general, any surface of the stage, or otherelement of the system that can be seen in both modeling andcolor-measurement images can be used as a reference plane.

In each of the color-measurement images, real position of elements ofthe cut stone in its image can first be identified, based on thecorresponding data obtained from the 3D model, and this identification,combined with the knowledge of the position of the reference plane, canallow applying a unified approach to the division of the images of thecut diamond in the color-measurement images into the above areas for afurther analysis of its color.

Geometrical or other considerations, based on which dimensions of thecentral and additional areas can be determined can be, for example,distances of the selected area from specific elements of the cut stoneor its boundaries.

Each of the central and/or additional areas can be defined by geometricdefinition of its location/size relative to a specific dimension/s ofthe cut diamond, such as e.g. the height of the pavilion in a round cutdiamond (i.e. the distance between the girdle and the culet of thediamond), its maximal width (the length of its girdle in a plan view) Inparticular, each area can be defined to extend between a fifth to athird of the maximal width of the cut diamond and/or between three andone quarters of a distance between a plane passing through the diamondat its location of a maximal width and its extremity disposed at amaximal distance from its table facet, such as a distance between therespective girdle and culet of a round cut stone. The additional areacan have the same height relative to the reference plane as the centralarea and can have a total length along this plane greater than that ofthe central area

For example, in the pavilion of a round cut diamond, the central areacan be selected to extend along a majority of the height of the stonebetween its girdle and culet, and optionally its spacing from the culetcan be greater than that from the girdle. The “central” area can also befound to be asymmetrical, or furthermore, non-contiguous and even notactually around the center of the stone but calculated by an alternativemethod that may apply analytical image processing tools.

The color indicative parameters can be used in any calculativecombination, e.g. using one or two-color indicative parameters from onearea with one or two-color indicative parameters from another area toobtain a color grading. The color grading can be a result of averaging anumber of such combinations.

FIGS. 2A to 2C each illustrate one color-measurement image taken by theimage sensor at the following respective angles mentioned above: 0°,30°, and 45, each including an image of a round cut diamond 705, animage of a stage 707 supporting it so that its girdle and pavilion aredisposed above the stage, an image of the background including abackground reference 708, and a reference plane 710. It is to beunderstood that the present invention is not limited to measurements atthe above angles and any other suitable angle or set of angles may beimplemented.

Referring to FIG. 2A, the image of the cut diamond 705 is shown thereinto be completely above the reference plane 710. In this image, the zonesof interest are an upper zone 700 constituting an upper selected area,and a lower zone 701 divided into a central area 702 and two peripheralareas 704 and 706 on two sides of the central area, the upper andperipheral areas constituting additional selected areas. The upper andlower areas are separated by a border line 703 and are selected so thateach extends along a third of the distance between the girdle and theculet. The upper third of said distance in this example is notconsidered as an area of interest. The central and peripheral areas areselected so that each extends along one third of this border line 703.In this specific example the upper area 700 and the central area 702each yield separate color indicative parameters while the peripheralareas 704 and 706 can be treated as a single additional area andtherefore yield color indicative parameters summarized from both areastogether.

In FIGS. 2B and 2C, the pavilion of the diamond as seen in therespective images thereof comprises only three selected areas, a centralarea 714, 720 and two peripheral areas 712 and 716, 718 and 722,respectively. The color indicative parameters derived from these imagesare obtained taking similar measures as elaborated above in connectionwith FIG. 2A.

Color assessment of a diamond can be performed in accordance with thisfirst embodiment as illustrated in FIG. 3.

First, a 3D model of the cut diamond is obtained in step 800. The 3Dmodel can be obtained, for example, by a modeling scanning of the cutstone. FIG. 3 shows one example of how a plurality of modeling imagesacquired at different positions of the diamond about the rotational axisof its stage in accordance with the teachings of the '961 patent oranother technique. An image sensor is then set in step 802 at a desiredangle of its optical axis relative to the horizon for color-measurementscanning of the cut diamond, which is then performed in step 804 by arelative movement of the cut diamond with respect to the image sensor,to capture color-measurement images of the cut diamond at differentpositions about the rotational axis of the stage. The scanning of thecut diamond in step 804 can be performed at a number of angularpositions of the image sensor and for each such position determined instep 806, steps 802 and 804 are repeated.

The captured images are sent in step 808 to an image processing devicewhich can be an image capturing module of the kind used in the systemdescribed in the aforesaid U.S. Pat. No. 9,519,961 or any otherprocessor, provided with an appropriate software for a further analysis.It should be noted that the images can be sent to the image processingafter any of the previous steps, for example immediately after beingcaptured or at the end of the color measurement scanning.

Steps 810 to 815 relate to the image processing. More particularly, instep 810 reference elements of the imaged cut diamond and/or its stageare identified in each image of interest for color grading, typicallybased on the obtained 3D model. Such elements can be boundaries of thecut diamond, the stage reference plane, the diamond's girdle and/orculet or the like. Once the reference elements are identified, areas inthe cut diamond are selected in step 812 based on geometricaldefinitions, such as distances between the reference elements. Eachselected area in the images contains data relating to color, namelycolor intensity values within the pixels assembling the selected area.These values are analyzed and calculated by methods known in the art toobtain at least one-color indicative parameter step 814. Steps 810, 812and 814 are repeated for each image that needs to be analyzed accordingto step 815.

A color grade of the cut diamond is calculated step 816 using theobtained color indicative parameters. The color grade is obtained by acalculative combination of different color indicative parameters fromdifferent areas, optionally giving each color indicative parameter adifferent weighting factor color.

While the above discussion details one method of measuring color byusing first a 3D volumetric measurement of the stone, followed byselective imaging of the stone, other ways may be utilized. In fact, a3D analysis may be eliminated altogether, so long as some methodology isutilized so that the stone' boundaries are known.

A Second Embodiment to Assess Stone Color

The hardware setup of the device used in connection with the presentinvention was briefly discussed above in connection with FIGS. 1A and1B. As discussed, two types of light sources are made to impinge on thestone, surrounding BBV light and also UV light sources mounted close tothe camera. While two types of light sources are shown and discussed, itis within the present invention to implement more than two types oflight sources. While two UV LEDs are shown in FIG. 1, it is to beunderstood that more than or for that matter less than two UV sourcesmay be implemented and used. Also, while the UV light sources areillustrated as being placed on either side of the camera in FIG. 1, itis to be understood that they may be placed within other areas in thecabinet shown in FIG. 1.

In operation, the stone may be homogeneously and diffusely illuminatedfrom all sides, by the LED pixeled panels, all of which may becontrolled independently. The illumination is made so that it is similarfrom all sides, as much as possible. The illumination may be controlledmanually or may be controlled automatically through the placement oflight sensors within the cabinet that are operatively connected to theprogrammable controller mentioned above. In operation, the user of thesystem may input, depending on the stone characteristics for example,different parameters of lighting schemes. These schemes may be developedempirically through use of the color system and stored in a non-volatilememory for use in discerning color of stones under test (SUT). Also,while it is expected that uniform, homogeneous, diffused illuminationwill be implemented to provide lighting by the LEDs, it may bepreferable in certain circumstances or conditions depending on the stoneitself to provide less homogeneous and more directional lighting by theLEDs.

BBV light can be white light, with sufficiently high correlated colortemperature (CCT) and sufficiently high color rendering index (CRI),which has an appropriate and satisfactory continuous representation forall visible wavelengths within the 400-700 nm range, and no significantgaps in the visible spectrum, D65-specified color or spectrum (daylightapproximation) are not necessary.

The light produced by the LEDs is not “daylight approximating” and isnot near the D65 standard. The D65 standard is known formally as CIEStandard Illuminant D65 and is a commonly used standard illuminant, eventhough there are not really any light sources that operate at thisstandard.

Returning now to FIG. 1, the stone may be first mounted on the rotatingstage 12 and then it is illuminated, while it is mounted on the rotatingstage in a table-down position, to ensure illumination through thestone's pavilion. The stone is then rotated by the rotating stage aroundits axis.

To improve the repeatability of the illumination and to produceconsistent measurement across a variety of stones, the stone ispreferably centered, that is, the stones' rotational symmetry axis orcenter of mass is aligned with the stage axis of rotation.

As mentioned above, in addition to BBV illumination using the LEDsdiscussed above, UV LEDs (365 nm) may be included in the optical setup,either directly illuminating the stone or illuminating the stoneindirectly through suitable lenses or reflector or both. Also, while UVlights of 365 nm wavelength are given above, it is to be understood thatUV lights of other wavelengths may be used and, as mentioned, more thanor less than two UV LEDs (of different wavelengths) may be implemented,and, further, may be mounted at positions within the cabinet at otherplaces than on either side of the camera.

The procedure for evaluating the color of a stone under test (SUT) maybe taken in two major steps, the first being data acquisition and thesecond being an analysis of the data acquired in the first step.

Step 1: Data Acquisition

As can be seen by referring to FIG. 1, the camera or sensor andassociated UV lights are mounted for rotation about an axis 20 thatallows the camera to capture images of the SUT at various angles. Thismay be accomplished while the SUT is stationary or as it is rotated bythe rotating stage 12.

The light from the impingement of the UV and other light sources iscollected by the sensor or camera 22 through its lens system. The cameraand the camera optics may be constructed so that even slight differencesin color may be distinguished.

In one embodiment example, the camera may take multiple pictures(frames) at each of the several different angular positions: 1. At 0°(normal to the rotation axis of the rotating stage 12) with BBVillumination; 2. At an elevation (towards the culet) with BBVillumination. 3. At a different, higher elevation (towards the culet)with BBV illumination. 4. At 0° (normal to the rotation axis) with UVillumination with power level 1.5. At 0° (normal to the rotation axis)with UV illumination with power level 2. Exemplary images taken at theseangles are illustrated in FIGS. 6A-6C.

It is to be appreciated that the several angles and application of twopower levels are only exemplary. Images may be captured at multipleangles, depending at least in part to the size and the shapecharacteristics of the SUT. For example, the “initial” angle may not be0 degrees at all, but something other than 0 degrees, dependent on thegeometry of the SUT, which in turn may be determined by 3D volumetricmodelling of the SUT. Also, more than or less than three angle imagecaptures may be obtained. Also, by employing multiple power levels, isconsidered only as optional, since as one power level may well suffice.

A total of 300 (or more, or less) images may be captured. It is to beunderstood that is not necessarily the minimal number nor a maximalnumber, and in theory, this number can be changed to suit thecharacteristics, for example, of the SUT. The images captured may thenbe stored in RAW format with no image processing (e.g., white balance)applied to those images. While the RAW format is the preferred format,the present invention is not limited to such format and other formatsmay be applied. The captured images may be stored in a suitable memorysystems or device under the control of the programmable controller.

Additionally, before data acquisition and as discussed above, the stonemay be scanned to create a 3D volumetric model of it (by using thetechniques discussed above such as the silhouette modeling method). Thismodel will be used to determine which of the pixels (in the futuremeasurement) are within the stone, and which are not. Also, the 3D modelmay determine the total (optimal) number of images, best appropriateangular elevations of the sensor and power levels of the BBV and UVillumination. This is due to the possibility of different optimalmethods for measurement of different 3D models (shape and size of thestone).

Further, Since the 3D volume and/or the geometry of the stone maydetermine and influence the images to be captured, the 3D model createdmay be utilized to provide the controller information with which toadjust one or more of the multiple angles set for the image capture. Inaddition, such model may be utilized to determine which of a pluralityof LEDs to activate or not activate.

Step 2: Data Analysis and Feature Extraction

As a first substep, the data acquired during step 1. above, consistingof raw images, may be then probed to recover the relevant pixels to beconsidered and analyzed.

First, the white reference is taken. The R, G, and B values are averagedto obtain the reference values for white balance of the specific frame.This may be performed only using BBV-illuminated pictures, and not forUV-illuminated pictures.

Second, the pixels within the stone may be selected by using theoptimized stone masks calculated from a 3D volumetric model, if employedearlier, and using, for example, the techniques disclosed in theaforesaid U.S. Pat. No. 9,519,961.

The stone pixels' colorimetric values are then calculated in thefollowing manner: It is noted that the calculation may use white balancecorrection for every frame.

For the UV-illuminated frames' R, G, and B values can be taken withoutany reference of calculation.

The stone pixels taken with BBV illumination can be differentiatedaccording to different histograms: one for each of the several (e.g.,three) camera angles, or, as mentioned above other suitable angles andin more than or less than three angles. The groups are separated byintensity levels for every camera angle (for all 60 frames).

It is to be noted here that the foregoing technique may be used in lieuof forming a 3D volumetric model of the stone, an example of whichtechnique is disclosed in the aforesaid U.S. Pat. No. 9,519,961mentioned just above.

For each group of pixels, the average color values given from the abovecalculations, standard deviations, and number of pixels for this groupis calculated

Additional to the BBV illumination light values, the UV-illuminated R,G, and B values, standard deviations, and number of pixels are added forboth UV intensities. Together, these are the featured values thatprovide the desirable information for the analysis of color in a givenSUT.

Additional values may be calculated from the UV features captured by thecamera: those of intensity and the color of fluorescence. Furthermore,these values could be used to grade SUT fluorescence, in line withwell-established manual methods.

All of the foregoing may be analyzed by a processor under the control ofthe programmed controller to provide a measure of the color of the SUT.

One key aspect of any measurement device is its ability to reproduceprevious results, otherwise termed “repeatability”. This is especiallythe case when grading diamond color, as even small variations can have asignificant effect on the price. As such, it would be of particularinterest to ensure that the conditions under which measurements occurare tightly controlled, namely the conditions governing the operation ofthe LEDs and imaging sensor. For both components, the primary source ofvariability has been shown to be temperature, which affects the gain andbackground noise of the sensor, and the power and wavelength of theLEDs. Therefore, in one embodiment, the temperature of the LEDs and ofthe imaging sensor are controlled via closed loop systems, such as, butnot limited to those based on thermoelectric cooling, phase changematerial, or resistive heating to a predefined, above ambienttemperature. In an additional embodiment, which can further be combinedwith the temperature control methods listed here, the temperature of theLEDs and sensor are monitored, and a correction is applied in softwarefor any changes. This correction can be implemented by any number ofstandard means, including, but not limited to, look up tables andanalytical functions.

In addition, as LED output can degrade over time, it is veryadvantageous to monitor this directly. Therefore, in another embodiment,which can also be implemented in conjunction with the methods listedabove, the device will include photodiodes dispersed throughout theenclosure to monitor the outputs of the LEDs. Changes in LED output canthen be corrected by any combination of: closed loop control of the LEDcurrents, changes to the camera gain and/or exposure time or multiplyingby a correction factor in software. Such correction can be applied toeither or both the visible light and the UV LEDs.

What we claim is:
 1. A system for the automatic grading of a stone undertest (SUT) comprising: an enclosure, the enclosure including a stage formounting the SUT, the stage comprising a stage rotation axis, the stagebeing configured to be rotatable about the stage rotation axis by arotation device; the enclosure further comprising one or more sources ofbroadband visible (BBV) light, the sources of BBV light beingcontrollable by a programmed controller; an image sensor for capturing aplurality of images of a mounted SUT; the image sensor being mounted onan arm, the arm being rotatable around a sensor elevation axis, thesensor elevation axis being normal to the stage rotation axis; one ormore sources of ultraviolet (UV) light mounted in the enclosure; wherebythe image sensor is programmed by the programmed controller to captureimages of the mounted SUT from one or more selected angles relative tothe position of the SUT on the stage rotation axis; the programmedcontroller being configured: to activate and control the power level ofone or more of the one or more sources of BBV light, to activate andcontrol the power level of one or more of the one or more sources of UVlight, to rotate the SUT around the stage rotation axis, and to causethe image sensor to capture one or more images of the cut/polished SUT;an image processing device configured to process the one or more imagescaptured by the image sensor and further configured to grade thecut/polished SUT using light indicative parameters from at least a partof the one or more images captured; characterized in that: the imagesensor being mounted on an arm, the arm being rotatable around a sensorelevation axis, the sensor elevation axis being normal to the stagerotation axis, the one or more sources of UV light mounted on the arm inthe vicinity of the image sensor, and the programmed controller alsobeing configured to rotate the arm around the sensor elevation axis andto activate and control the image sensor to capture images of themounted SUT from one or more selected angles relative to the sensorelevation axis.
 2. The system of claim 1, wherein the programmedcontroller is configured to scan the SUT prior to the programmedcontroller being configured to capture images for grading, the scan ofthe SUT causing the programmed controller to create a 3D volumetricmodel of the SUT.
 3. The system of claim 1, wherein the programmedcontroller is configured to: average the color-space values, for two ormore captured images, of the one or more captured images to calculatereference values of white balance of the one or more captured images. 4.The system of claim 1, further comprising the programmed controllerbeing configured to, if a 3D volumetric model of the SUT has beencreated, select pixels and differentiate the selected pixels either by:(a) creating histograms for the selected pixels captured at thedifferent angular positions and by the programmed controller beingconfigured to divide the selected pixels by their levels of intensity,whereby the average color is calculated, (b) segmenting the SUT intodistinct regions, and using selected pixels captured within saidregions, at the different angular positions, whereby the average coloris calculated.
 5. The system of claim 1, further comprising theprogrammed controller being configured to calculate colorspace values ofthe one or more images of the SUT under the one or more UV lightsources, the programmed controller further being configured to add thecalculations under UV light to average color calculations from the oneor more BBV sources and wherein color grading is corrected based uponmeasurement under UV illumination.
 6. The system of claim 4, furthercomprising the programmed controller being configured to compare theaverage color calculation of a SUT to a calibrated lookup tablecontaining data on calibrated SUTs with known SUT whiteness and to matchthe SUT calculations to those of the calibrated SUTs to determine agrade level of the SUT.
 7. The system of claim 1, wherein the programmedcontroller is further configured to grade the SUT to take into accountthe simultaneous contrast effect.
 8. The system of claim 4, wherein if a3D volumetric model has been created, the programmed controller isconfigured to use the 3D volumetric model to one or more of: (a) adjustone or more of multiple angles set for image capture, (b) determinewhich of a plurality of sources of UV light to activate, (c) determinewhich of a plurality of sources of BBV light to activate, and (d)determine the intensity at which to activate each of the selected BBV/UVsources.
 9. The system of claim 1, wherein the temperature of one ormore of the BBV light sources and/or the one or more of the UV lightsources are actively controlled.
 10. The system of claim 5, wherein themeasurement under UV illumination is also used for grading thefluorescence of the SUT.
 11. A method for the automatic grading of astone under test (SUT) comprising: providing an enclosure, the enclosureincluding a stage for mounting the SUT, the holder comprising a centralaxis, the stage being rotatable about a stage rotation axis by arotation device; the enclosure further comprising one or more sources ofbroadband visible light (BBV), the sources of BBV light beingcontrollable by a programmed controller; providing an image sensor forcapturing a plurality of color-measurement images of a SUT mounted onthe stage; providing one or more sources of UV light mounted in theenclosure; providing an image processing device configured to processthe plurality of images and to grade the cut/polished SUT using lightindicative parameters from at least a part of the one or more imagescaptured; wherein the method further comprises: capturing by the imagesensor, images of the mounted SUT from one or more selected anglesrelative to the position of the SUT on the stage rotation axis;activating and controlling the power level of one or more of the one ormore sources of BBV light, rotating the SUT around the stage rotationaxis, and causing the image sensor to capture one or more images of thecut/polished SUT; processing the one or more images; and, grading thecut/polished SUT using light indicative parameters from at least a partof the one or more images captured; characterized in that: the imagesensor being mounted on an arm, the arm being rotatable around a sensorelevation axis, the sensor elevation axis being normal to the stagerotation axis, the one or more sources of UV light mounted on the arm inthe vicinity of the image sensor, and the programmed controller alsobeing configured to rotate the arm around the sensor elevation axis andto activate and control the image sensor to capture images of themounted SUT from one or more selected angles relative to the sensorelevation axis.
 12. The method of claim 11, further comprising theprogrammed controller scanning the SUT prior to the programmedcontroller capturing light in the form of images, the scanning of theSUT causing the programmed controller to create a 3D volumetric model ofthe SUT.
 13. The method of claim 11, wherein the programmed controller:for the plurality of captured images, averaging the color-space valuesof one or more captured images to calculate reference values of whitebalance of the one or more captured images.
 14. The method of claim 11,further comprising the programmed controller, if a 3D volumetric modelof the SUT has been created, selecting pixels and differentiating theselected pixels either by: (a) creating histograms for the selectedpixels captured at the different angular positions and by the programmedcontroller dividing the selected pixels by their levels of intensity,whereby the average color is calculated, (b) segmenting SUT ontodistinct regions, and using selected pixels captured within saidregions, at the different angular positions, whereby the average coloris calculated.
 15. The method of claim 11, further comprising theprogrammed controller calculating color-space values of the one or morecaptured images of the SUT under the one or more UV light sources, theprogrammed controller further adding the calculations under UV light tothe average color calculations from the one or more BBV sources, whereincolor grading is corrected based upon measurement under UV illumination.16. The method of claim 14, further comprising the programmed controllercomparing the average color calculations of a SUT to a calibrated lookuptable containing data on calibrated SUTs with known SUT whiteness andmatching the SUT calculations to those of the calibrated SUTs todetermine a grade level of the SUT.
 17. The method of claim 11,comprising the further step wherein grading the SUT further adjusts thegrade calculation taking into account the simultaneous contrast effect.18. The method of claim 14, further comprising the steps of theprogrammed controller using the 3D volumetric model one or more of: (a)adjusting one or more of multiple angles set for image capture, (b)determining which of a plurality of sources of UV light to activate, (c)determining which of a plurality of sources of BBV light to activate,and (d) determining the intensity at which to activate each of theselected BBV/UV sources.
 19. The method of claim 11, wherein thetemperature of one or more of the UV light sources and/or the one ormore of the BBV light sources are is actively controlled.
 20. The methodof claim 11, wherein the measurement under UV illumination is also usedto grade the fluorescence of the SUT.